Tuesday, April 16, 2013

I was pulling together a presentation on what to expect after the drought of 2012. After a quick search, I came across the following article by John Hartman from the March 6th, 2006 Kentucky Pest Newsletter. It was so well written, I decided to share it with you in our blog. I think we will see the same landscape diseases after the drought of 2012.

From March 6, 2006 Kentucky
Pest Newsletter

HOW WILL THE DROUGHT OF 2005
AFFECT LANDSCAPE PLANT DISEASES? By John Hartman

Much of the bluegrass and
eastern parts of Kentucky
suffered dry weather during 2005. Rainfall in most Kentucky locations was below normal every
month except January and August. August would have been more deficient except
for the rainy aftermath of Hurricanes Dennis and Katrina. Indeed, the Bluegrass
region suffered moderate to severe drought for most of the summer and eastern Kentucky was in a state
of severe drought by summer's end. Even now, in late winter, Bluegrass
and eastern regions are in a state of mild drought. Woody plants. Wilt and leaf scorch symptoms are
often associated with dry weather. In addition, drought-stressed plants close
their stomata which reduces their rate of photosynthesis. Reduction in
photosynthesis may not kill a tree or shrub, but it means fewer carbohydrates
are made and stored for future use. In the landscape, seedlings and recently
transplanted trees and shrubs were at greatest risk because they lacked
extensive root systems. With drought, there are some
fungal diseases of landscape trees and shrubs that often do not show symptoms
until the following season, after the drought has passed. The role of water
stress in encouraging opportunistic plant pathogens is unclear. It is possible
that the stress condition interferes with the plant's defense against such
pathogens, or possibly, the reduced carbohydrate reserve allows the plant
little energy to fight invasion by pathogens. Expect certain fungi such as Hypoxylon, primarily an
oak pathogen, and Armillaria,
which attacks many woody plants, to appear in 2006 because of the 2005 drought
stress. In addition expect symptoms of diseases caused by other fungi such as Thyronectria, (honey
locust canker); Cytospora
or Valsa,
(cankers on prunus, poplar, willow, maple, spruce and other conifers); Diplodia, (pine tip
blight); and Botryosphaeria
and Nectria
(cankers of many woody plants such as rhododendrons, crabapples, dogwoods,
maples, and others) to appear the season following the dry weather. In searching for water, some
woody plants could have sacrificed surface roots to the drought while relying
more heavily on roots that were deeper in the soil. If excessive rains return,
partial flooding could render these deeper roots more prone to root rot
diseases, thus leaving the woody plants with few functional roots. Thus, expect
additional woody plant death when the drought breaks. One possible benefit of the
drought could be the reduction in foliar diseases this year. There could be
less carry-over inoculum from shade tree anthracnose diseases, crabapple scab
or rose black spot, for example. The benefit could be short-lived, however if
spring weather is wet and rapidly repeating cycles of these diseases occur.
Looking ahead even farther, the rust infections of cedar that should have
occurred, but didn't, during the dry 2005 summer might result in fewer cedar
galls in the spring of 2007 and less rust on crabapples and hawthorns that same
summer. Herbaceous
ornamentals.
Perennial flowers and ground covers, like their woody counterparts could have
reduced energy reserves due to the drought. This could make them more
susceptible to cankers and to root, corm, or bulb rot diseases. There is not
much research on the role of stress on diseases of herbaceous ornamentals, so
it is difficult to know how the drought will affect these plants. A few
diseases such as Volutella blight of Pachysandra, are known to be more severe
on stressed plants, but most likely the disease would have appeared during the
drought. For foliar diseases, the situation is similar to that of woody plants
- reduced primary inoculum might result in less disease, at first. Tree fruits. Tree fruits in the landscape and
orchard are subject to many of the same diseases as shade trees. Fungi such as
Nectria, Cytospora and Botryosphaeria cause cankers of tree fruits suffering
from drought stress. The effects are likely to be the same as for landscape
trees. As for reduced inoculum for foliar diseases such as apple scab or cherry
leaf spot, again the response should be about the same as for landscape trees. Small fruits. Blueberries and brambles in the
garden are especially susceptible to fungal cankers, and grapes also can become
cankered. They are likely to react to drought in a similar way as woody
landscape plants. Reduced foliar diseases could also be expected for these
crops, at first. Strawberries that were not watered probably died last summer
from lack of water or from the black root rot complex which is usually more
severe on drought-stressed crops. On the other hand, if they did survive, this
season could bring a reduced threat from leaf spot and anthracnose diseases, at
least at first.

"Japanese
spurges are particular about their growing sites so select a good site
carefully. They will not grow well in full sun or in poorly drained
areas."

If too much sun is a problem, you may want to try to transplant it to a better location that suits its growing needs.

Unfortunately, a "stressed" plant can lead to disease and pests! I found some scale ( Oystershell Scale - Lepidosaphes) on
the stems of these plants, but I do not think this is the main problem.

When people see pests, they jump to conclusions and assume that they are the problem! Well, if the plant is stressed from not being planted in the proper site, pests like these scales, could become a full blown infestation.

"The first line of defense against insect and mite pests of ornamental
landscape plants is to select adapted plants that are not known to
develop perpetual pest problems. Plant ornamental plants in suitable
locations and care for them properly to avoid plant stress conditions."